The ultimate goal of this project is to gain an understanding of the mechanism(s) by which the pigment epithelium interacts with and supports the normal functioning of the neural retina. The immediate goals are to describe the ion transport mechanisms of the pigment epithelium in both cold-blooded and mammalian preparations and show how they are related to the activity of the neural retina. The disturbance of these mechanisms may be one of the main reasons for the loss of vision which follows pigment epithelial disease and/or detachment of the neural retina from the pigment epithelium. These goals can be reformulated in terms of two questions. First, what are the ionic mechanisms by which pigment epithelial cells transport water, salts, metabolites and catabolites between the choroidal blood and the neural retina? Second, in what ways do pigment epithelial cells interact with the photoreceptors through these ionic mechanisms and do alterations in these ionic mechanisms affect photoreceptor activity in the light and dark? It is proposed to study these interactions with a combined electrophysiological and epithelial transport approach. Ion fluxes will be measured across isolated preparations of frog pigment epithelium-choroid. Pigment epithelial membrane potentials will be recorded intracellularly in response to changes in the concentrations of extracellular ions. Similar experiments will be performed on intact retinal preparations. A mammalian pigment epithelium-choroid preparation will be developed and studied in a similar manner.